Hot-gas reciprocating engine



Oct. 21, 1958 c. o. JONKERS 2,857,220

' HOT-GAS RECIPROCATING ENGINE Filed Jan. 14, 1955 15 3E 26 /7 1 w P k? /7 .51 23 19' INVENT'OR CORNELIUS OTTO JONKERS AGENT United States Patent HOT-GAS RECIPROCATING ENGINE Cornelius Otto Jonkers, Emmasingel, Eindhoven, Netherlands, assignor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application January 14, 1955, Serial No. 481,871

Claims priority, application Netherlands January 22, 1954 Claims. (Cl. 309-) The invention relates to a hot-gas reciprocating engine, constructed in the form of a displacer-piston engine. The term hot-gas reciprocating engine is to be understood to mean herein a hot-gas motor, a cold-gas refrigerator and a heat pump, the latter two machines operating on the reversed hot-gas engine principle.

'It is known that it is of great importance with these machines that no or at least only a small quantity of lubricant should penetrate into the working space of the machine, since the lubricant may be carried along by the working medium of the machine to the heat exchangers, more particularly to the regenerator. Then the lubricant may be deposited in these machine parts, so that the heat transfer in the heat exchangers decreases, which affects adversely the output and the specific power of the machine. The regenerator, which is often constructed as a wire generator, having a wire diameter of less than 100 may even be completely obturated.

It is known to provide pistons or piston rods with a special groove which is intended to prevent as far as possible the lubricant from being transported to the working space of the machine. A different solution for the aforesaid problem of the oil transport along two reciprocating parts has been found and this solution may be applied particularly with success to the piston of a displacerpiston machine. The piston of the displacer-piston machine is the piston body which acts upon the total volume of the working space in the machine.

According to the invention the piston of this displacerpiston machine tapers towards the top end from a point where a free circulation of the medium in the gap between the piston and the associated cylinder with the crank case can take place, so that in normal operation of the machine between the piston and the cylinder wall a conical gap is is provided, the conicity of which at the periphery is at least 0.01 and at the most 0.1"; the largest sectional area of this gap lies at the top end and on the side of the largest sectional area the gap merges with a widening second gap, which is at least substantially conical, the conicity of this second gap exceeding that of the first gap. The term conicity of the gap is to be understood to mean herein half the apex of the conical piston surface.

It the piston is not provided with a scraping ring which conveys back to the crank case the scraped-off lubricant through a separate duct in the piston, it may be desirable that the conical gap, the conicity of which lies within the aforesaid limits, should extend to the bottom of the piston. However, if provision is made of such a scraping ring, the conicity may start from this scraping ring. The second conical gap is intended, more particularly, to prevent oil from being scraped off the cylinder wall by the piston, and from being collected on the piston. In one embodiment of the invention it is desirable that the second cone extends at least to a point where the dis tance between the piston wall associated with the second cone and the prolongation of the piston wall associated with the first cone should be at least equal to the largest difference in diameter between the wall of the first cone and the cylinder wall, while the second cone has a conicity of not more than 3.

The distance between the wall of the second conical part of the piston and the prolongation of the first conical part must be measured in a plane at right angles to the centre line of the piston. The gap must be taken on an average along the periphery of the piston, the piston being assumed to lie centrally in the cylinder.

It will often be desirable that the piston should be provided with piston rings. According to one aspect of the invention, these piston rings are provided in the first conical part of the piston. In the second part of the piston which is adjacent the first conical part no piston rings are provided.

According to a further aspect of the invention it is desirable that these piston rings should bear on the cylinder wall during normal operation of the machine in a manner such that between a ring and the cylinder wall a conical gap is formed, having its largest sectional area at the top end. A conicity of a direction opposite to that of the piston must particularly be avoided,

It should be noted that it is already known to use a conical gap in conjunction with a scraping device lying over it in order to prevent oil from being transported along a piston moving up and down. It has been found, however, that for the piston described above a particular conical gap even without such a scraping edge sufiices to prevent lubricant from penetrating into the working space of the machine.

The invention will now be described with reference to a few embodiments.

Fig. 1 shows a hot-gas reciprocating engine, constructed in the form of a displacer-piston machine,

Fig. 2 shows one embodiment of a piston, and

Fig. 3 shows a further embodiment of a piston.

The hot-gas reciprocating engine shown in Fig. l is a cold-gas refrigerator, which comprises a cylinder 1, in which a displacer piston 2 and a piston 3 move up and down with substantially constant phase difference. The displacer-piston 2 acts upon the volume of the space 4, the lower-temperature space, also termed the freezing space, and upon the volume of the space 5, the highertemperature space, also termed the cooled space. The piston 3 acts'upon the volume of the space 5. The spaces 4 and 5 are in open communication with one another through a freezer 6, a regenerator 7 and a cooler 8. Owing to the reciprocating movements of the piston and the displacer piston, expansion occurs mainly in the space 4 and compression mainly in the space 5. The displacer piston 2 is coupled through a connecting rod system 9 with a crank shaft 10 and the piston 3 is coupled through a connecting-rod system 11 with cranks of the same crank shaft 10. The refrigerator is driven by an electric motor 12. The piston 3 has a conicity of at least 001 and of not more than 0.l through the major part of its height and a part has a larger conicity.

Fig. 2 shows on a larger scale part of the piston 3, the conicity being shown larger for the sake of clearness than is desirable in accordance with the invention. This piston does not exhibit a scraping ring and the conicity extends to the bottom of the piston. In the part 13, which has a conicity of at least 001 and at the most 0.1" and which has its largest sectional area at the top end, provision is made of a plurality of piston rings 15, which bear on the cylinder 'wall 16 in a manner such that a conical gap 17 is formed between a ring and the cylinder wall, the largest sectional area 18 of this gap lying at the top end.

Owing to the conical shape of the part 13 no lubricant or only a small quantity of lubricant is transported upwards, since any lubricant conveyed along is pumped down during. the upward stroke of the pistonv owing to the conical shape of the piston. A second conical part 19, which lies over the conical part 13, is intended to prevent oil =whichz may: be.scraped ofibthe cylinderswallr from: reachingi-the::top.of the'vpistonm This conical: part v extends so far that the distance 20fibetween.,the. Wall-10f thisepart iandwthe prolongation: of the wall-of the .conical .part 13* is-at least. equal ttortheudiiference between the diameterh21-E of the-cone 13:and-ztheadiametern" of the cylindeiwwall.v Theconicityofithe part 19'exceeds that/of the partr13, but it'is at:the :most 3.

With the pistonshown in 1Fig.: 3 provisionds made. of a scraping; spring 23; the t-lu-bricant scrapedtoff by. it is conveyed; back to the=crank ca-se .throughcducts::24 land 25-.in the pistonhwall: The conicalrpart 13"thusextends fromithisrscrapingzringz: The conical part 13is adjacent a part. 26, which-:is substa-nti-a-llynconical andvis slightly rounded off in this case, the conicity exceeding that of r the part-r13, but being-:at-the-rnost.3l- Also intthisicase the. distance 20"is at=least equaL-to the difference between thediarneters-ZLand 22.- I

What is claimed is:- I

1. Ina hot-gas reciprocatingomachine a cylinder,:;and

at least one piston. adapted .-to reciprocate in-said cy1in'der, said pistonzhaving a firstpart-angularly disposedin1rela-l tion. to said cylinder-wall to form a firsttconical::gap between said first pistonv parti and theradjacent cylinder wall;t

:13, the: largest: seetionalt area:ofathegaprbeingson the up- I per end of 'saidpistonzpart, saidpiston having a secondpart more angularly disposed toward:said-first cylinder wallthan-:said first part to thereby forrn a second conical-gap Cir which has a conicity exceeding that of said firstconical. gap.

2. In a hot-gas reciprocating machine the combination as set forth in claim 1 wherein the distance between the second part of saidt-pistonand the adjacent piston wall is at least equal to the largest diiference in distance between the walltof. said first piston part and'the adjacentcylinder wall, said second part of the piston having a conicity of not more than-3 3. In a hot-gas reciprocating machine thecombination as claimed in claim 1 further comprising a plurality-of piston rings on said first part of the piston.

4. In-a hot-gas reciprocating machine the'combination as set forth .inrclaim 3 wherein said piston rings bear:on adjacent portions of said cylinder wall to form a conical gap between each ring and the adjacent portions of said cylinder wall, said conical gap having its largest sectional area at the top' end thereof.

5. 111:8. hot-gas reciprocating machine the combination:

asrset forth in claim 4:further comprising a scraping element provided on said piston, said scraping element haveingchannels for conducting awaythe scrapedeoff lubri-, 

